An unexpected snowstorm hit Swiss Alps on Sunday, April 29, 2018, trapping at least 14 people in the Pigne d’Arolla area and forcing them to spend the night outdoors in the high winds and snow.

The police in Valais, southwestern Switzerland said it launched a major relief operation and sent 7 helicopters to rescue the hikers after receiving a call from a manager of a rest-stop at dawn on Monday.

“Four people lost their lives and five others are in a critical state,” the police said in a statement. One of them was found dead while the other 3 died in hospital.

Officials said the group had set out from the Dix rest-stop and had been trying to reach Vignettes hikers hut at 3 157 m (10 357 feet) on a route called The Serpentine when they were caught off-guard by the storm.

The police later said that two more hikers were found dead further east.